336 MEXICAN BOUNDARY SHELLS— BALL. 



PATULA STRIGOSA var. CONCENTRATA, Dall. 

 Patuhi xtrinosa var. roncentrata, Dall, Proc. U. S. Nat. Miis., XVIII, p. 1, 1895. 



A variety, which exactly mimics tlie normal form above meutioued, 

 has the same number of whorls, but measures only 13 mm. in minor 

 and 1(» in major diameter, with a heijiht of 8 mm. Its coloration, when 

 not bleached, is usually a dark-brown band above and below and a 

 white peripliery. It was found in some numbers on the summits of 

 Hachita and the lluachuca Mountains, and preserves a marked uni- 

 formity, which would seem to entitle it to a varietal imme. 



Type. — No. 129909, TJ.S.N.M. Also on the Jemez ]\Iountains, Ashmun. 



The peculiarly arid climate, with irregular rainfall, which character- 

 izes the region where these snails are found, is probably responsible 

 for the vivii)arity which distinguishes them from the I*<(fnla' of moister 

 regions. The young shells exist in the oviduct of the parent, in num- 

 bers from 4 to 8, and reach a development of more than 2 whorls ami 

 a diameter of nearly 5 mm. before extrusion. AVhen born they are 

 quite able to take care of themselves, and can if necessary form a pro- 

 tective epiphragm at once. The soft-shelled eggs laid by the eastern 

 species of Fatuht would doubtless dry up completely in an hour or two 

 in the dry atmosphere of Arizona. 



Family HELICID^. 



Genus THYSANOPHORA, Strebel and Pfeffer. 



THYSANOPHORA HORNII, Gabb. 



A single dead specimen (No. 130001, U.S.aST.M.) was sent in by Dr. 

 Mearns, collected at the summit of the Hachita Grande Mountain, 

 Grant County, Xew Mexico. The species was originally described 

 from the vicinity of Fort Grant, Arizona, and is a characteristic species 

 of the region. I have seen it from the drift of the Yaqui River, Mexico. 

 When fresh it is translucent, dark brownish, the periostracum with 

 oblique raised spiny lamella? Inclined at an angle to the incremental 

 lines. This coating seems to have a certain sticky (piality, so that grains 

 of dirt adhere to it with such persistency that the shell can not be 

 cleaned without destroying the periostracum. Dead specimens are 

 rather solid, coarsely striated, and chalky-looking, hardly to be recog- 

 nized as the same thing. 



It occurs by some oversight in Pilsbry's revision of the Helices in 

 the lists under both PyramiduJa and TIn/sanopliora. Without a knowl- 

 edge of the anatomy its ])roper place can not be determined, but the 

 aspect of the shell is more like some of the Tliysanophoriv than 

 Pyramidula, 



